Hydraulic circuit device of hydraulic working machine

ABSTRACT

To permit smooth performance of both of an operation requiring a high pressure and an operation desired to produce a pressure at a suppressed level, a shuttle block positioned between pilot operating units and flow control valves and pump regulators is arranged in association with shuttle valves, which select maximum pressures of groups of operation signal pressures produced by the pilot operating units, respectively, and at least one of the plural groups of operation signals, and is constructed to include hydraulic selector valves and a boom-lowering, hydraulic selector valve that are operable in particular ways.

TECHNICAL FIELD

The present invention relates to a hydraulic circuit system for ahydraulic working machine such as a hydraulic excavator, and moreparticularly to a hydraulic circuit system for hydraulic working machinein which the maximum pressure of plural operation signals generated by aplurality of pilot operating units is detected by a shuttle valve, andthe thus-detected maximum pressure is used as a control signal pressureto operate a control device such as a regulator for a hydraulic pump.

BACKGROUND ART

As conventional art of this type, there is one disclosed in JP 11-082416A.

According to this conventional technique, a hydraulic circuit systemwhich is for arrangement, for example, in a hydraulic working machine isprovided with at least one hydraulic pump, for example, two hydraulicpumps; plural actuators driven by hydraulic fluids delivered from thesehydraulic pumps, for example, a right track motor, a left track motor, aswing motor, a boom cylinder, an arm cylinder and a bucket cylinder;plural flow control valves for feeding the hydraulic fluids, which havebeen delivered from the hydraulic pumps, respectively, to theabove-mentioned plural actuators; a pilot hydraulic pressure source, andplural pilot operating units for producing operation signal pressuresfrom the pilot hydraulic pressure source to change over thecorresponding flow control valves.

The hydraulic circuit system also has shuttle valves for selectingmaximum pressures of plural groups of operation signal pressures amongthe operation signal pressures produced by the above-mentioned pluralpilot operating units; hydraulic selector valves arranged in associationwith the plural groups of operation signal pressures to operate based onthe maximum pressures such that corresponding control signal pressuresare produced from the pressure of the pilot hydraulic pressure andsource and are outputted as pump control signals or the like; and ashuttle block with all of the above-mentioned shuttle valves and theabove-mentioned hydraulic selector valves built therein.

The hydraulic circuit system is constructed such that it produces theabove-mentioned control signal pressures in the shuttle block and by thecontrol signal pressures, operates one or more operation devicesarranged in association with any one or more of the hydraulic pumps,actuators and flow control valves, for example, one or more regulatorsfor the hydraulic pump or pumps.

As the conventional technique constructed as described above is providedin the shuttle block with the plural shuttle valves and produces,produces in the shuttle block the control signal pressures for operatingthe operation devices, and outputs the control signal pressures, pipingis no longer needed between the shuttle valves so that the constructionof the circuit can be simplified. Accordingly, the hydraulic circuitsystem assures an improvement in assembly workability, can minimizelosses upon transmission of signal pressures, and can operate controldevices such as regulators with good responsibility.

With the above-described conventional technique, however, when the flowcontrol characteristics of the regulators for the hydraulic pumps aredetermined in conformity with boom-raising operations, travelingoperations and the like each of which requires a high pressure even whenoperated delicately, the delivery flow rate of the pumps increase evenin a boom-raising operation or superstructure-swinging operation inwhich it is not desired to produce a pressure too much. As aconsequence, the pressure becomes high, so that the operability of theboom-raising operation or superstructure-swinging operation isdeteriorated to lead to a reduction in the accuracy of work performed bythe hydraulic working machine. When the flow control characteristics ofthe regulators for the hydraulic pumps are conversely determined toproduce a pressure at a suppressed level with a view to improving theoperability of a boom-raising operation or superstructure-swingingoperation, the operability of various operations which require highpressures such as boom-raising operations and traveling operations isdeteriorated, resulting in a problem that the accuracy of various workperformed by the hydraulic working machine is lowered.

The present invention has been completed in view of the reality of theabove-described conventional technique, and has an object thereof theprovision of a hydraulic circuit system for a hydraulic working machine,which can smoothly perform both of an operation requiring a highpressure and an operation which desires the production of a pressure ata suppressed level.

DISCLOSURE OF THE INVENTION

To achieve the above-described object, the present invention provides ahydraulic circuit system for a hydraulic working machine, said hydrauliccircuit system comprising at least one hydraulic pump, plural actuatorsdriven by a hydraulic fluid delivered from the hydraulic pump, pluralflow control valves for feeding the hydraulic fluid, which has beendelivered from the hydraulic pump, to the plural actuators,respectively, a pilot hydraulic pressure source, plural pilot operatingunits for producing operation signal pressures from the pilot hydraulicpressure source to change over the corresponding flow control valves,shuttle valves for selecting maximum pressures from plural groups ofoperation signal pressures among the operation signal pressures producedby the plural pilot operating units, a hydraulic selector valve arrangedin association with at least one of the plural operation signal pressuregroups and operated based on the maximum pressure to produce acorresponding control signal pressure from the pressure of the pilotpressure source, and a shuttle block with all of the shuttle valves andhydraulic selector valve built therein such that the control signalpressures are produced in the shuttle block to operate at least onecontrol device arranged in association with any one of the hydraulicpump, the actuators and the flow control valves, wherein in addition tothe hydraulic selector valve operated based on the maximum pressure, atleast one of a boom-lowering, hydraulic selector valve, which isoperated based on an operation signal pressure relating to a singleboom-lowering operation among the operation signal pressures produced bythe pilot operating units, and a superstructure-swinging, hydraulicselector valve, which is operated based on an operation signal pressurerelating to a swing revolving operation to produce a swing controlsignal pressure from the pressure of the pilot pressure source, is builtin the shuttle block.

According to the present invention constructed as described above, whena boom-lowering, hydraulic selector valve is provided, for example, theboom-lowering, hydraulic selector valve, upon performing a singleboom-lowering operation, is changed over responsive to an operationsignal pressure relating to a boom-lowering operation, and aboom-lowering control signal pressure is produced in the shuttle blockand is outputted to an operation device, for example, a regulator forthe hydraulic pump. Accordingly, the regulator is operated such thatfrom the hydraulic pump, a hydraulic fluid is delivered at a flow ratecommensurate with the boom-lowering control signal pressure.

When a superstructure-swinging, hydraulic selector valve is provided,for example, the superstructure-swinging, hydraulic selector valve, uponperforming a single superstructure-swinging operation, is changed overresponsive to an operation signal pressure relating to asuperstructure-swinging operation, and a swing control signal pressureis produced in the shuttle block and is outputted to an operationdevice, for example, the regulator for the hydraulic pump. Accordingly,the regulator is operated such that from the hydraulic pump, a hydraulicfluid is delivered at a flow rate commensurate with the swing controlsignal pressure.

Upon performing an operation other than such a single boom-loweringoperation or single superstructure-swinging operation as describedabove, for example, the maximum pressure of a group of operation signalpressures relating to the operation is selected through the pluralshuttle valves, and responsive to the maximum pressure, a hydraulicselector valve different from the above-mentioned boom-lowering,hydraulic selector valve or superstructure-swinging, hydraulic selectorvalve is changed over such that a corresponding control signal pressureis produced in the shuttle block and is outputted to an operationdevice, for example, the regulator for the hydraulic pump.

Therefore, the regulator is operated such that from the hydraulic pump,a hydraulic fluid is delivered at a flow rate commensurate with thecontrol signal pressure outputted based on the above-mentioned maximumpressure.

If the regulator is, for example, of such a type that it operates todeliver a hydraulic fluid at a higher flow rate from the hydraulic pumpas the applied control signal pressure becomes higher, presetting isperformed such that the value of a boom-lowering control signal pressureoutputted with a change-over operation of the boom-lowering, hydraulicselector valve or the value of a superstructure-swinging, control signalpressure outputted with a change-over operation of thesuperstructure-swinging, hydraulic selector valve becomes lower than thevalue of a control signal pressure outputted with a change-overoperation of the hydraulic selector valve operated based on theabove-mentioned maximum pressure.

As a consequence, upon performing an operation which requires a highpressure, a control signal pressure outputted with a change-overoperation of a hydraulic selector valve operated based on the maximumpressure of the group of operation signal pressures relating to therelevant operation is applied to the regulator so that the regulator isoperated to increase the flow rate of the hydraulic pump and hence, thehigh-pressure operation can be performed. Upon performing a singleboom-lowering operation or a single superstructure-swinging operation,in other words, an operation which desires to produce a pressure at asuppressed level, a boom-lowering control signal pressure orsuperstructure-swinging control signal pressure outputted with achange-over operation of the boom-lowering, hydraulic selector valve orsuperstructure-swinging, hydraulic selector valve is applied to theregulator so that the regulator is operated to suppress the flow rate ofthe hydraulic pump and hence, the single boom-lowering operation orsingle superstructure-swinging operation, which desires the productionof a pressure at a suppressed level, can be performed.

According to the present invention, it is, therefore, possible tosmoothly perform both of an operation, which requires a high pressure,and a single boom-lowering operation or superstructure-swingingoperation, which desires the production of a pressure at a suppressedlevel, and hence, to assure good operability.

When constructed as mentioned above, the control signal pressuresproduced from the boom-lowering, hydraulic selector valve andsuperstructure-swinging, hydraulic selector valves may comprise apressure signal for operating the control device arranged in associationwith the hydraulic pump.

In this case, with respect to equal operation signal pressures from thepilot operating units, a delivery flow rate from the hydraulic pumpbased on control signal pressures produced from the boom-loweringselector valve and superstructure-swinging, hydraulic selector valvesmay be smaller than a delivery flow rate from the hydraulic pump basedon a control signal pressure produced from another hydraulic selectorvalve for operating the control device arranged in association with thepump.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a hydraulic excavator shown as an example of ahydraulic working machine in which the hydraulic circuit systemaccording to any one of embodiments of the present invention can beinstalled.

FIG. 2 is a hydraulic circuit diagram illustrating the overallconstruction of a first embodiment of the hydraulic circuit systemaccording to the present invention, which is installed in the hydraulicexcavator shown in FIG. 1.

FIG. 3 is a hydraulic circuit diagram depicting flow control valves andactuators arranged in the first embodiment of the present inventionillustrated in FIG. 2.

FIG. 4 is a hydraulic circuit diagram showing pilot operating units forchanging over the flow control valves depicted in FIG. 3.

FIG. 5 is a hydraulic circuit diagram illustrating a shuttle blockarranged in the first embodiment shown in FIG. 2.

FIG. 6 is a characteristic diagram illustrating pilot pressure(operation signal pressure) and pump control signal characteristicsavailable from the first embodiment of the present invention.

FIG. 7 is a characteristic diagram illustrating pilot pressure(operation signal pressure) and pump flow rate characteristics availablefrom the first embodiment of the present invention.

FIG. 8 is a hydraulic circuit diagram depicting a shuttle block whichconstitutes an essential part of a second embodiment of the presentinvention.

FIG. 9 is a hydraulic circuit diagram depicting a shuttle block whichconstitutes an essential part of a third embodiment of the presentinvention.

BEST MODES FOR CARRYING OUT THE INVENTION

The embodiments of the hydraulic circuit system according to the presentinvention for the hydraulic working machine will hereinafter bedescribed based on the drawings.

FIG. 1 is the side view of the hydraulic excavator shown as an exampleof the hydraulic working machine in which the hydraulic circuit systemaccording to any one of the embodiments of the present invention can beinstalled.

The hydraulic excavator is provided with a lower travel base 100, anupper swing superstructure 101, and a work front 102. Right and lefttrack motors 16,21 are mounted on the lower travel base 100 torotationally drive respective crawlers 100 a, whereupon the excavatortravels forward or rearward. A swing motor 18 which will be describedsubsequently herein is mounted on the upper swing superstructure 101 toswing the upper swing superstructure 101 rightwards or leftwardsrelative to the lower travel base 100. The work front 102 is made up ofa boom 103, an arm 104 and a bucket 105. The boom 103 is verticallypivoted by a boom cylinder 20, the arm 104 is operated by an armcylinder 19 toward a dumping (open) side or a crowding (filling) side,and the bucket 105 is operated by a bucket cylinder 17 toward thedumping (open) side or the crowding (filling) side.

FIGS. 2 through 5 are illustrations of the first embodiment of thepresent invention, in which FIG. 2 is the hydraulic circuit diagramillustrating the overall construction of the first embodiment of thehydraulic circuit system according to the present invention, which isinstalled in the hydraulic excavator shown in FIG. 1, FIG. 3 is thehydraulic circuit diagram depicting the flow control valves and theactuators arranged in the first embodiment of the present inventionillustrated in FIG. 2, FIG. 4 is the hydraulic circuit diagram showingpilot operating units for changing over the flow control valves depictedin FIG. 3, and FIG. 5 is the hydraulic circuit diagram illustrating theshuttle block arranged in the first embodiment shown in FIG. 2.

As shown in FIG. 2, this first embodiment is provided with mainhydraulic pumps 1 a, 1 b, a pilot pump 2, an engine 3 for rotationallydriving the pumps 1 a, 1 b and 2, and a valve unit 4 connected to themain hydraulic pumps 1 a,1 b. The valve unit 4 has two valve groups,i.e., a group of flow control valves 5-8 and a group of flow controlvalves 9-13. The flow control valves 5-8 are positioned on a centerbypass line 15 a which is connected to a delivery line 14 a of the mainhydraulic pump 1 a, while the flow control valves 9-13 are positioned ona center bypass line 15 b which is connected to a delivery line 14 b ofthe main hydraulic pump 1 b.

The main hydraulic pumps 1 a, 1 b are variable displacement pumps ofswash plate type, and these hydraulic pumps 1 a, 1 b are provided withregulators 28 a, 28 b for controlling tiltings of respective swashplates, i.e., displacements.

A pilot relief valve 31 for holding a delivery pressure of the pilotpump 2 at a constant pressure is connected to a delivery line 30 of thepilot pump 2. The pilot pump 2 and the pilot relief valve 31 jointlyconstitute a pilot hydraulic source.

The flow control valves 5-8 and 9-13 of the valve unit 4 are changedover by operation signal pressures from pilot operating units 35,36,37.The pilot operating units 35,36,37 generate respective operation signalpressures based on the delivery pressure (constant pressure) of thepilot pump 2 as a source pressure.

The operation signal pressures generated by the pilot operating units35,36,37 are once introduced into a shuttle block 50, and then appliedto the flow control valves 5-8 and 9-13 through the shuttle block 50 asshown in FIG. 2. Based on the operation signal pressures from the pilotoperating units 35,36,37, a front operation signal Xf, a track operationsignal Xt and pump control signals XP1, XP2 are produced in the shuttleblock 50 as will be mentioned below. For example, the pump controlsignals XP1, XP2 are outputted as control signal pressures to pumpregulators 28 a,28 b through signal lines 52,53, respectively.

As shown in FIG. 3, the flow control valves 5-8 and 9-13 included in thevalve unit 4 are of the center bypass type.

Hydraulic fluids delivered from the main hydraulic pumps 1 a,1 b aresupplied to corresponding one or more of the actuators through theseflow control valves 5-13. The actuators consist of the right track motor16, the bucket cylinder 17, the swing motor 18, the arm cylinder 19, theboom cylinder 20, and the left track motor 21.

The flow control valve 5 is for the right track, the flow control valve6 is for the bucket, the flow control valve 7 is for the first boom, theflow control valve 8 is for the second arm, the flow control valve 9 isfor swing, the flow control valve 10 is for the first arm, the flowcontrol valve 11 is for the second boom, the flow control valve 12 isfor reserve, and the flow control valve 13 is for the left track.Namely, the two flow control valves 7, 11 are provided for the boomcylinder 20 and the two flow control valves 8, 10 are provided for thearm cylinder 19 such that the hydraulic fluids from the two hydraulicpumps 1 a, 1 b are combined together and fed to the boom cylinder 20 andthe arm cylinder 19.

As illustrated in FIG. 4, the pilot operating unit 35 consists of apilot operating device 38 for the right track and a pilot device 39 forthe left track. These pilot operating devices are provided with pairs ofpilot valves (reducing valves) 38 a,38 b;39 a,39 b and control pedals 38c,39 c, respectively. When the control pedal 38 c is trod in theback-and-forth direction, one of the pilot valves 38 a,38 b is operateddepending on the direction of the treading, and an operation signalpressure Af or Ar is produced depending on the stroke of the treading.When the control pedal 39 c is trod in the back-and-forth direction, oneof the pilot valves 39 a,39 b is operated depending on the direction ofthe treading, and an operation signal pressure Bf or Br is produceddepending on the stroke of the treading. The operation signal pressureAf is used for moving the right track forward and the operation signalpressure Ar is used for moving the right track rearward, whereas theoperation signal pressure Bf is used for moving the left track forwardand the operation signal pressure Br is used for moving the left trackrearward.

The pilot operating unit 36 consists of a pilot operating device 40 forthe bucket and a pilot operating device 41 for the boom. These pilotoperating devices comprise pairs of pilot valves (reducing valves) 40a,40 b;41 a,41 b, respectively, and a common control lever 40 c. Whenthe control lever 40 c is manipulated in the left-and-right direction,one of the pilot valves 40 a,40 b is operated depending on the directionof the manipulation, and an operation signal pressure Cc or Cd isproduced depending on the stroke of the manipulation. When the controllever 40 c is manipulated in the back-and-forth direction, one of thepilot valves 41 a,41 b is operated depending on the direction of themanipulation, and an operation signal pressure Du or Dd is produceddepending on the stroke of the manipulation.

The operation signal pressure Cc is used for crowding the bucket and theoperation signal pressure Cd is used for dumping the bucket, whereas theoperation signal pressure Du is used for raising the boom and theoperation signal pressure Dd is used for lowering the boom.

The pilot operating unit 37 consists of a pilot operating device 42 forthe arm and a pilot operating device 43 for swing.

These pilot operating devices comprise pairs of pilot valves (reducingvalves) 42 a,42 b;43 a,43 b, respectively, and a common control lever 42c. When the control lever 42 c is manipulated in the left-and-rightdirection, one of the pilot valves 42 a,42 b is operated depending onthe direction of the manipulation, and an operation signal pressure Ecor Ed is produced depending on the stroke of the manipulation. When thecontrol lever 42 c is manipulated in the back-and-forth direction, oneof the pilot valves 43 a,43 b is operated depending on the direction ofthe manipulation, and an operation signal pressure Fr or Fl is produceddepending on the stroke of the manipulation. The operation signalpressure Ec is used for crowding the arm and the operation signalpressure Ed is used for dumping the arm, whereas the operation signalpressure Fr is used for swinging the upper swing superstructure to theright and the operation signal pressure Fl is used for swinging it tothe left.

The shuttle block 50 shown in FIG. 5 is provided with a main unit 60,shuttle valves 61-63,65-75,90,91 which are built in the main unit 60,hydraulic selector valves 81,82 operated responsive to the maximumpressure in a group of operation signal pressures relating to variousoperations, and boom-lowering, hydraulic selector valve 83 operatedresponsive to an operation signal pressure Dd relating to a boomlowering operation.

The shuttle valves 61-63,65-67 are disposed in an upstream stage of ashuttle valve group. The shuttle valve 61 selects the higher one of theoperation signal pressure Af for moving the right track forward and theoperation signal pressure Ar for moving the right track rearward. Theshuttle valve 62 selects the higher one of the operation signal pressureBf for moving the left track forward and the operation signal pressureBr for moving the left track rearward. The shuttle valve 63 selects thehigher one of the operation signal pressure Cc for crowding the bucketand the operation signal pressure Cd for dumping the bucket. The shuttlevalve 65 selects the higher one of the operation signal pressure Ec forcrowding the arm and the operation signal pressure Ed for dumping thearm. The shuttle valve 66 selects the higher one of the operation signalpressure Fr for swinging the upper swing superstructure to the right andthe operation signal pressure Fl for swinging it to the left.

The shuttle valve 67 selects the higher one of operation signalpressures from a pair of pilot valves of a reserve pilot operating unitwhich is arranged when a reserve actuator is connected to the reserveflow control valve 12.

The shuttle valves 68-70 are disposed in a second stage of the shuttlevalve group. The shuttle valve 68 selects the higher one of theoperation signal pressures selected by the shuttle valves 61,62 in thefirst stage. The shuttle valve 69 selects the higher one of theoperation signal pressure Du for raising the boom and the operationsignal pressure selected by the shuttle valve 65 in the most upstreamstage. The shuttle valve 70 selects the higher one of the operationsignal pressures selected by the shuttle valves 66,67 in the mostupstream stage.

The shuttle valves 71,72 are disposed in a third stage of the shuttlevalve group. The shuttle valve 71 selects the higher one of theoperation signal pressures selected by the shuttle valve 63 in the mostupstream stage and the shuttle valve 69 in the second stage. The shuttlevalve 72 selects the higher one of the operation signal pressuresselected by the shuttle valves 69,70 in the second stage.

The shuttle valves 73,74 are disposed in a fourth stage of the shuttlevalve group. The shuttle valve 73 selects the higher one of theoperation signal pressures selected by the shuttle valve 61 in the mostupstream stage and the shuttle valve 71 in the third stage. The shuttlevalve 74 selects the higher one of the operation signal pressuresselected by the shuttle valves 71,72 in the third stage.

The shuttle valve 75 is disposed in a fifth stage of the shuttle valvegroup and selects the higher one of the operation signal pressuresselected by the shuttle valve 62 in the most upstream stage and theshuttle valve 72 in the third stage.

The hydraulic selector valve 81 disposed in a downstream stage of theshuttle valve 73 in the fourth stage is changed over by the applicationof the operation signal pressure, which has been selected by the shuttlevalve 73, to a pressure receiving parts 81 a, and produces acorresponding control signal pressure from the pressure of the pilotpump 2.

Further, the hydraulic selector valve 82 disposed in a downstream stageof the shuttle valve 75 is changed over by the application of theoperation signal pressure, which has been selected by the shuttle valve75, to a pressure receiving part 82 a produces a corresponding controlsignal pressure from the pressure of the pilot pump 2.

The boom-lowering, hydraulic selector valve 83 disposed in addition tothese hydraulic selector valves 81,82 is changed over by the applicationof the operation signal pressure Dd, which relates to a boom-loweringoperation, to a pressure receiving part 83 a, produces a correspondingboom-lowering control signal pressure from the pressure of the pilotpump 2.

The external dimensions of the above-mentioned hydraulic selector valves81,82 and boom-lowering, hydraulic selector valve 83, including theirsprings, are set equal, for example.

However, the cross-sectional area of a line 83 b in the boom-lowering,hydraulic selector valve 83 communicating a line 85, which is incommunication with the pilot pump 2, and a line 87, which is incommunication with a line 86 between the shuttle valves 90 and 91, isset smaller beforehand compared with the cross-sectional areas of lines81 b,82 b in the hydraulic selector valves 81,82. As illustrated in FIG.6, owing to this setting, the characteristics of the boom-lowering,hydraulic selector valve 83 are represented by characteristics S2 whichhave been parallelly shifted downwards relative to characteristics S1 ofthe control signal pressure outputted responsive to an operation signalpressure Pi applied to the pressure receiving parts 81 a,82 b of thehydraulic selector valves 81,82, that is, the pump control signal XP1(XP2). Namely, when the level of the operation signal pressure Pi isequal, the values of control signal pressures outputted from theboom-lowering, hydraulic selector valve 83 (the pump control signalsXP1,XP2) become lower compared with the values of control signalpressures outputted from the boom-raising, hydraulic selector valves81,82 (the pump control signals XP1,XP2).

Returning again to FIG. 5, a description will now be made.

In the most downstream stage, the shuttle valves 90,91 are disposed. Ofthese, the shuttle valve 90 selects the higher one of the control signalpressure produced at the hydraulic selector valve 81 and theboom-lowering, control signal pressure produced at the boom-lowering,hydraulic selector valve 83, and outputs it as the pump control signalXP1.

The shuttle valve 91 selects the higher one of the control signalpressure produced at the hydraulic selector valve 82 and the controlsignal pressure produced at the boom-lowering, hydraulic selector valve83, and outputs it as the pump control signal XP2.

Incidentally, the operation signal pressure selected by the shuttlevalve 68 is outputted as the track operation signal Xt, and is used forcontrolling the track system. On the other hand, the operation signalpressure selected by the shuttle valve 74 is outputted as the frontoperation signal Xf, and is used for controlling driving of the workfront 102.

The pump control signals XP1,XP2 outputted from the shuttle valves90,91, respectively, are fed to the pump regulators 28 a,28 b via thesignal lines 52,53 illustrated in FIG. 2. Namely, the pump regulators 28a,28 b control the delivery flow rates of the hydraulic pumps 1 a,1 b inaccordance with the values of the pump control signals XP1,XP2.

Operations in the first embodiment constructed as described above willhereinafter be described.

[Individual Operations Except for a Single Boom-lowering Operation]

When at least one of the pilot operating unit 38 for the right track,the pilot operating unit 40 for the bucket, the pilot operating unit 41when used in a boom raising operation, for example, and the pilotoperating unit 42 for the arm is manipulated, the correspondingoperation signal pressure is applied to the corresponding one of theflow control valves 5-8.

In the case of one operation signal pressure, the operation signalpressure is applied to the pressure receiving part 81 a of the hydraulicselector valve 81, and in the case of plural operation signal pressures,the maximum one of the plural operation signal pressures is selected bythe shuttle valves 61,63,65,69,71,73 and is applied to the pressurereceiving part 81 a of the hydraulic selector valve 81. As a result, thehydraulic selector valve 81 is changed over, and a control signalpressure is outputted from this hydraulic selector valve 81 and isoutputted as the pump control signal XP1 to the regulator 28 a for themain hydraulic pump 1 a through the shuttle valve 90. The regulator 28 ahas such a characteristic that the tilting of the main hydraulic pump 1a is increased, for example, as the pressure of the pump control signalXP1 rises. Upon application of the pump control signal XP1, theregulator 28 a increases the delivery rate of the main hydraulic pump 1a in accordance with the pump control signal XP1. As a result, one ormore of the flow control valves corresponding to the one or moreoperation signal pressures are changed over, and the hydraulic fluid isdelivered from the main hydraulic pump 1 a at a flow rate correspondingto the operation signal pressure. The hydraulic fluid is fed to thecorresponding one or more of the right track motor 16, the bucketcylinder 17, the arm cylinder 19 and the boom cylinder 20 such thatthese actuators are driven.

When at least one of the pilot operating unit 39 for the left track, thepilot operating unit 41 when used in a boom raising operation, forexample, the pilot operating unit 42 for the arm, and the pilotoperating unit 43 for swing is manipulated, the corresponding operationsignal pressures is applied to the corresponding one of the flow controlvalves 9, 10 and 11. In the case of one operation signal pressure, theoperation signal pressure is applied to the pressure receiving part 82 aof the hydraulic selector valve 82, and in the case of plural operationsignal pressures, the maximum one of the plural operation signalpressures is selected by the shuttle valves 62,65,66,69,70,72,75 and isapplied to the pressure receiving part 82 a of the hydraulic selectorvalve 82. As a result, the hydraulic selector valve 82 is changed over,and is outputted as the pump control signal XP2 to the pump regulator 28b through the shuttle valve 91. Like the regulator 28 a, the pumpregulator 28 b also has such a characteristic that the tilting of themain hydraulic pump 1 b is increased, for example, as the pressure ofthe pump control signal XP2 rises. Upon application of the pump controlsignal XP2, the regulator 28 b increases the delivery rate of the mainhydraulic pump 1 b in accordance with the pump control signal XP2. As aresult, one or more of the flow control valves corresponding to the oneor more operation signal pressures are changed over, and the hydraulicfluid is delivered from the main hydraulic pump 1 b at a flow ratecorresponding the operation signal pressure. The hydraulic fluid is fedto the corresponding one or more of the swing motor 18, the arm cylinder19, the boom cylinder 20 and the left track motor 21 such that theseactuators are driven.

When at least one of the pilot operating unit 40 for the bucket, thepilot operating unit 41 when used in a boom raising operation, the pilotoperating unit 42 for the arm, and the pilot operating unit 43 for swingis manipulated, the corresponding operation signal pressure is appliedto the corresponding one of the flow control valves 6, 7, 8, 9, 10 and11. In the case of one operation signal pressure, the operation signalpressure is outputted as the front operation signal Xf, and in the caseof plural operation signal pressures, the maximum one of the pluraloperation signal pressures is selected by the shuttle valves63,65,66,69,70,71,72,74, and then outputted as the front operationsignal Xf.

When at least one of the pilot operating unit 40 for the bucket, thepilot operating unit 41 when used in a boom raising operation, the pilotoperating unit 42 for the arm, and the pilot operating unit 43 for swingis additionally manipulated with intent to carry out a combinedtrack/front operation under a condition where the pilot operating unit38 for the right track and the pilot operating unit 39 for the lefttrack have been manipulated, the corresponding operation signalpressures are applied to the flow control valves 5, 13 and thecorresponding one or more of the flow control valves 6, 7, 8, 9, 10 and11.

The maximum one of the operation signal pressures from the pilotoperating unit 40 for the bucket, the pilot operating unit 41 when usedin a boom raising operation, the pilot operating unit 42 for the arm,and the pilot operating unit 43 for swing is selected by the shuttlevalves 63,65,66,69,70,71,72,74, and then outputted as the frontoperation signal Xf.

Further, when at least one of all the pilot operating operations exceptfor the operation of the pilot operating device when used in a boomraising operation (operations of the pilot operating unit 38 for theright track, the pilot operating unit 39 for the left track, the pilotoperating unit 40 for the bucket, the pilot operating unit 41 when usedin a boom raising operation, the pilot operating unit 42 for the arm,and the pilot operating unit 43 for swing) is performed, thecorresponding operation signal pressure is applied to the correspondingone of the flow control valves 5-11 and 13. In addition, when at leastone of the pilot operating unit 38 for the right track and the pilotoperating unit 39 for the left track is manipulated, the maximum one ofthe operation signal pressures is selected by the shuttle valves61,62,68 and outputted as the track operation signal Xt.

Also, when at least one of the pilot operating unit 40 for the bucket,the pilot operating unit 41 when used in a boom raising operation, thepilot operating unit 42 for the arm, and the pilot operating unit 43 forswing is manipulated, the maximum one of their operation signalpressures is output as the front operation signal Xf as described above.

[Single Boom-lowering Operation]

Especially when the pilot operating device 41 is operated upon a singleboom-lowering operation, the corresponding operation signal pressure Ddis applied to the flow control valves 7,11 and further, the operationsignal pressure Dd is applied to the pressure receiving part 83 a of theboom-lowering, hydraulic selector valve 83 housed in the shuttle valve50 depicted in FIG. 5. As a result, the hydraulic selector valve 83 ischanged over, the boom-lowering control signal pressure is outputtedfrom this boom-lowering, hydraulic selector valve 83, and through therespective shuttle valves 90,91, the pump control signal XP1,XP2 areoutputted to the pump regulators 28 a,28 b through the signal lines52,53.

When the single boom lowering operation is effected over a similarstroke as the individual operations other than the single boom loweringoperation, the values of the pump control signals XP1,XP2 at this timebecome, as shown in FIG. 6, lower compared with the values of the pumpcontrol signals XP1,XP2 outputted through the hydraulic selector valves81,82 in association with the other individual operations. As indicatedby the characteristics K2 in FIG. 7, the flow rates delivered from themain hydraulic pumps 1 a,1 b controlled by the pump regulators 28 a,28b, therefore, tend to be suppressed compared with the characteristics K1when the pump regulators 28 a,28 b are controlled by the pump controlsignals XP1,XP2 outputted through the hydraulic selector valves 81,82.As a consequence, the pressure produced in the boom cylinder 20 can becontrolled to a suppressed low pressure. As has been described above,the first embodiment can perform well a single boom lowering operationwhich is desired to be performed while controlling the pressure at asuppressed level.

As has been mentioned above, the first embodiment permits smoothperformance of both of an operation requiring a high pressure, saidoperation being other than a single boom lowering operation, and thesingle boom lowering operation desired to produce a pressure at asuppressed level, assures good operability, and can improve the accuracyof various work performed by the hydraulic excavator.

FIG. 8 is the hydraulic circuit diagram depicting the shuttle blockwhich constitutes the essential part of the second embodiment of thepresent invention.

In this second embodiment, a shuttle valve 64 which selects the higherone of a boom-raising operation signal pressure Du and a boom-loweringoperation signal pressure Dd is disposed in the most upstream stageinside the shuttle block 50. The pressure selected by the shuttle valve64 is applied to the shuttle valve 69 which is also arranged in thefirst embodiment.

In particular, the second embodiment is provided with asuperstructure-swinging, hydraulic selector valve 84 in addition to thehydraulic selector valves 81,82 which are changed over responsive to thehigher pressures selected by the shuttle valves 73,75. By theapplication of an operation signal pressure, which is selected at theshuttle valve 60 and relates to swinging, to the pressure receiving part84 a, this superstructure-swinging, hydraulic selector valve 84 ischanged over such that from the pressure of the pilot pump 2, acorresponding superstructure-swinging control signal pressure isproduced.

In a downstream stage of the hydraulic selector valve 82 and thesuperstructure-swinging, hydraulic selector valve 84, a shuttle valve 92is arranged to select the higher one of control signal pressure producedat the hydraulic selector valve 82 and a superstructure-swinging controlsignal pressure produced at the superstructure-swinging, hydraulicselector valve 84 and then, to output a pump control signal XP2.

The external dimensions of the above-mentioned hydraulic selector valves81,82 and superstructure-swinging, hydraulic selector valve 84,including their springs, are set equal, for example. However, thecross-sectional area of a line 84 b in the superstructure-swinging,hydraulic selector valve 84 communicating the line 85, which is incommunication with the pilot pump 2, and a line 88, which is incommunication with the shuttle valve 92, with each other is set smallerbeforehand compared with the cross-sectional areas of the lines 81 b,82b in the hydraulic selector valves 81,82. As illustrated in FIG. 6,owing to this setting, the characteristics of thesuperstructure-swinging, hydraulic selector valve 84 are represented bycharacteristics S2 which have been parallelly shifted downwards relativeto characteristics S1 of the pump control signals XP1,XP2 outputted fromthe hydraulic selector valves 81,82.

The remaining construction is similar to that of the above-describedfirst embodiment.

In the second embodiment constructed as described above, describing, forexample, about operations of the pump regulators 28 a,28 b, a pumpcontrol signal XP1 which is a control signal pressure produced at thehydraulic selector valve 81 is applied to the pump regulator 28 athrough a signal line 52 in each of the operations other than the singlesuperstructure-swinging operation. Further, a pressure selected at theshuttle valve 92, specifically a pump control signal XP2 which is thehigher one of the control signal pressure produced at the hydraulicselector valve 82 and a superstructure-swinging control signal pressureproduced at the superstructure-swinging, hydraulic selector valve 84 isapplied to the pump regulator 28 b through the signal line 53. By thepump control pressure, the pump regulators 28 a,28 b control thedelivery flow rates from the main hydraulic pumps 1 a,1 b. The values ofthe pump control signals XP1,XP2 at this time are located on thecharacteristics S1 in FIG. 6 as mentioned above. On the other hand, thevalues of the flow rates Q of the main hydraulic pumps 1 a,1 bcontrolled by the pump regulators 28 a,28 b, respectively, are locatedon the characteristics K1 in FIG. 7.

In a single superstructure-swinging operation, thesuperstructure-swinging control signal pressure produced at thesuperstructure-swinging, hydraulic selector valve 84 is outputted as thepump control signal XP2 through the shuttle valve 92, and is applied tothe pump regulator 28 b. As a result, the pump regulator 28 b controlsthe flow rate to be delivered from the main hydraulic pump 1 b. Thevalue of the pump control signal XP2 at this time is located on thecharacteristics S2 in FIG. 6 as mentioned above. Namely, the value ofthe pump control signal XP2 at this time is lower compared with thevalue of the pump control value XP2 during the operations other than thesingle superstructure-swinging operation.

Therefore, the value of the flow rate Q of the main hydraulic pump 1 bcontrolled by the pump regulator 28 b is located on the characteristicsK2 in FIG. 7, and tends to be suppressed compared with thecharacteristics K1 of the case that the regulator 28 b is controlled bythe pump control signal XP2 outputted through the hydraulic selectorvalve 82. As a consequence, the pressure produced at the swing motor 18can be controlled to a suppressed low pressure. As readily appreciatedfrom the foregoing, the second embodiment can perform well a single boomlowering operation which is desired to be performed while controllingthe pressure at a suppressed level.

As has been described above, the second embodiment permits smoothperformance of both of an operation requiring a high pressure, saidoperation being other than a single superstructure-swinging operation,and the single superstructure-swinging operation desired to produce apressure at a suppressed level, assures good operability, and canimprove the accuracy of various work performed by the hydraulicexcavator.

FIG. 9 is the hydraulic circuit diagram depicting the shuttle blockwhich constitutes the essential part of the third embodiment of thepresent invention.

This third embodiment is a combination of the above-described firstembodiment and second embodiment.

Specifically, a shuttle block 50 is internally provided with aboom-lowering, hydraulic selector valve 83 and asuperstructure-swinging, hydraulic selector valve 84 in addition to ahydraulic selector valve 81 and a hydraulic selector valve 82. Theboom-lowering, hydraulic selector valve 83 is changed over by theboom-lowering, operation signal pressure Dd, thesuperstructure-swinging, hydraulic selector valve 84 is changed over bythe operation signal pressure Fr or F1 selected by the shuttle valve 66and relating to swinging, the hydraulic selector valve 81 is changedover by a higher pressure selected by a shuttle valve 73, and thehydraulic selector valve 82 is changed over by a higher pressureselected by a shuttle valve 75. In a downstream stage of the shuttlevalve 91, there is disposed a shuttle valve 93 which selects the higherone of the pressure selected by the shuttle valve 91 and thesuperstructure-swinging control signal pressure produced by thesuperstructure-swinging, hydraulic selector valve 84 and outputs it as apump control signal XP2.

The external dimensions of the above-mentioned hydraulic selector valves81,82, boom-lowering hydraulic selector valve 83 andsuperstructure-swinging, hydraulic selector valve 84, including theirsprings, are set equal, for example. However, the cross-sectional areaof a line 83 b in the boom-lowering, hydraulic selector valve 83communicating the line 85, which is in communication with the pilot pump2, and a line 87, which is in communication with a line 86 between theshuttle valves 90 and 91, with each other is set smaller beforehandcompared with the cross-sectional areas of the lines 81 b,82 b in thehydraulic selector valves 81,82. Further, the cross-sectional area of aline 84 b communicating a line 85, which is in communication with thepilot pump 2, and a line 89, which is in communication with the shuttlevalve 93, with each other set smaller beforehand compared with thecross-sectional areas of the flow lines 81 b,82 b in the hydraulicchange-over valves 81,82.

As illustrated in FIG. 6, owing to this setting, the characteristics ofthe boom-lowering, hydraulic selector valve 83 and the characteristicsof the superstructure-swinging, hydraulic selector valve 84 arerepresented by characteristics S2 which have been parallelly shifteddownwards relative to characteristics S1 of the pump control signalsXP1,XP2 outputted from the hydraulic selector valves 81,82.

The remaining construction is similar to that of the above-describedfirst embodiment.

In the third embodiment constructed as described above, describing, forexample, about operations of the pump regulators 28 a,28 b, a controlsignal pressure produced at the hydraulic selector valve 81 is outputtedas a pump control signal pressure XP1 to a signal line 52 through ashuttle valve 90 and is applied to the pump regulator 28 a in each ofthe operations other than the single boom-lowering operation and thesingle superstructure-swinging operation. Further, a control signalpressure produced at the hydraulic changeover valve 82 is outputted as apump control signal XP2 to a signal line 53 through a shuttle valve 91and is applied to the pump regulator 28 b.

By the pump control signal pressures, the pump regulators 28 a,28 bcontrol the delivery flow rates from the main hydraulic pumps 1 a,1 b.The values of the pump control signals XP1,XP2 at this time are locatedon the characteristics S1 in FIG. 6 as mentioned above. On the otherhand, the values of the flow rates Q of the main hydraulic pumps 1 a,1 bcontrolled by the pump regulators 28 a,28 b, respectively, are locatedon the characteristics K1.

In a single boom-lowering operation, a boom-lowering control signalpressure produced at the boom-lowering, hydraulic selector valve 83 isoutputted as pump control signals XP1,XP2 through the shuttle valve90,91,93, and are applied to the pump regulators 28 a,28 b,respectively. As a result, the pump regulators 28 a,28 b control thedelivery flow rates from the main hydraulic pumps 1 a,1 b. The values ofthe pump control signals XP1,XP2 at this time are located on thecharacteristics S2 in FIG. 6. Namely, the values of the pump controlsignal XP1,XP2 at this time are lower compared with the values of pumpcontrol values XP1,XP2 during each of the operations other than thesingle boom-lowering operation and the below-described, singlesuperstructure-swinging operation. Therefore, the values of flow rates Qof the main hydraulic pumps 1 a,1 b controlled by the regulators 28 a,28b are located on the characteristics K2 in FIG. 7, and tend to besuppressed compared with the characteristics K1 of the case that theregulators 28 a,28 b are controlled by pump control signal XP1,XP2outputted through the hydraulic selector valves 81,82. As a consequence,a pressure produced at the boom cylinder 20 can be controlled to asuppressed low pressure.

In a single superstructure-swinging operation, a superstructure-swingingcontrol signal pressure produced at the superstructure-swinging,hydraulic selector valve 84 is outputted as a pump control signal XP2through the shuttle valve 93, and is applied to the pump regulator 18 b.As a result, the pump regulator 28 b controls the delivery flow ratefrom the main hydraulic pump 1 b. The value of the pump control signalXP2 at this time is located on the characteristics S2 in FIG. 6.

Namely, the value of the pump control signal XP2 at this time is lowercompared with the value of the pump control value XP2 during each of theoperations other than the above-mentioned, single boom-loweringoperation and single superstructure-swinging operation. Therefore, thevalue of a flow rate Q of the main hydraulic pump 1 b controlled by thepump regulator 28 b is located on the characteristics K2 in FIG. 7, andtends to be suppressed compared with the characteristics K1 of the casethat the regulator 28 b is controlled by a pump control signal XP2outputted through the hydraulic selector valves 81,82. As a consequence,a pressure produced at the swing motor 18 can be controlled to asuppressed low pressure.

As has been described above, the third embodiment permits smoothperformance of both of an operation requiring a high pressure, saidoperation being other than a single boom-lowering operation and a singlesuperstructure-swinging operation, and the single boom-loweringoperation or single superstructure-swinging operation desired to producea pressure at a suppressed level, assures good operability, and canimprove the accuracy of various work performed by the hydraulicexcavator.

In each of the above-described embodiments, the cross-sectional area ofthe line 83 b formed in the boom-lowering, hydraulic selector valve 83or the cross-sectional area of the line 84 b formed in thesuperstructure-swinging, hydraulic selector valve 84 is set smallerbeforehand compared with the cross-sectional areas of the flow lines 81b,82 b formed in the hydraulic selector valves 82,82. The presentinvention is, however, not limited to such a construction.

For example, it is possible to adopt such a construction that theexternal dimensions of the hydraulic selector valves 81,82, the externaldimensions of the boom-lowering, hydraulic selector valve 83 and theexternal dimensions of the superstructure-swinging, hydraulic selectorvalve 84, all including the lines 81 b,82 b,83 b,84 b, are set equal toeach other and a spring having stronger spring force than those ofsprings biasing spools of the hydraulic selector valves 81,82 isarranged on the boom-lowering, hydraulic selector valve 83 or thesuperstructure-swinging, hydraulic selector valve 84.

The characteristics of pump control signals XP1,XP2 upon a singleboom-lowering operation or a single superstructure-swinging operationwhen constructed as described above become those represented by thecharacteristics S3 in FIG. 6. Specifically, the inclinations of theircharacteristics lines become gentler compared with the characteristicsS1 of the pump control signals XP1,XP2 corresponding to the controlsignal pressures produced at the hydraulic selector valves 81,82. Asshown by the characteristics K3 in FIG. 7, the values of the flow ratesQ of the main hydraulic pumps 1 a,1 b tend to be suppressed comparedwith the characteristics K1 when the regulators 28 a,28 b are controlledby the pump control signals XP1,XP2 corresponding to the control signalpressures produced at the hydraulic selector valves 81,82. As aconsequence, a pressure to be produced at the boom cylinder 20 or theswing motor 18 can also be controlled to a suppressed low pressure.

Similarly to the above-described individual embodiments, theconstruction which takes into consideration the force of the springbiasing the spool of the boom-lowering, hydraulic selector valve 83 orthe superstructure-swinging, hydraulic selector valve 84 as describedabove also permits smooth performance of both of an operation requiringa high pressure, said operation being other than a single boom-loweringoperation and a single superstructure-swinging operation, and the singleboom-lowering operation or single superstructure-swinging operationdesired to produce a pressure at a suppressed level, assures goodoperability, and can improve the accuracy of various work performed bythe hydraulic excavator.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to smoothly performboth of an operation requiring a high pressure and an operation desiredto produce a pressure at a suppressed level, and further, to improve theaccuracy of various work performed by a hydraulic working machine, inwhich the hydraulic circuit system can be installed, over theconventional art.

1. A hydraulic circuit system for a hydraulic working machine, saidhydraulic circuit system comprising: at least one hydraulic pump, pluralactuators driven by a hydraulic fluid delivered from said hydraulicpump, plural flow control valves for feeding the hydraulic fluid, whichhas been delivered from said hydraulic pump, to said plural actuators,respectively, a pilot hydraulic pressure source, plural pilot operatingunits for producing operation signal pressures from said pilot hydraulicpressure source to change over the corresponding flow control valves,shuttle valves for selecting maximum pressures from plural groups ofoperation signal pressures among the operation signal pressures producedby said plural pilot operating units, a hydraulic selector valvearranged in association with at least one of said plural operationsignal pressure groups and operated based on said maximum pressure toproduce a corresponding control signal pressure from the pressure of thepilot pressure source, and a shuttle block with all of said shuttlevalves and hydraulic selector valve built therein such that said controlsignal pressures are produced in said shuttle block to operate at leastone control device arranged in association with any one of saidhydraulic pump, said actuators and said flow control valves, wherein inaddition to said hydraulic selector valve operated based on said maximumpressure, at least one of a boom-lowering, hydraulic selector valve,which is operated based on an operation signal pressure relating to asingle boom-lowering operation among said operation signal pressuresproduced by said pilot operating units, and a superstructure-swinging,hydraulic selector valve, which is operated based on an operation signalpressure relating to a swing revolving operation to produce a swingcontrol signal pressure from the pressure of said pilot pressure source,is built in said shuttle block, wherein said control signal pressuresproduced from said boom-lowering, hydraulic selector valve andsuperstructure-swinging, hydraulic selector valves comprise a pressuresignal for operating said control device arranged in association withsaid hydraulic pump, and wherein with respect to equal operation signalpressures from said pilot operating units, a delivery flow rate fromsaid hydraulic pump based on control signal pressures produced from saidboom-lowering selector valve and superstructure-swinging, hydraulicselector valves are smaller than a delivery flow rate from saidhydraulic pump based on a control signal pressure produced from anotherhydraulic selector valve for operating said control device arranged inassociation with said pump.